The steel industry produces more waste materials than any other manufacturing business. For example, approximately 120 million tons of steel per year are produced in North America and this, in turn, produces about 12 million tons of waste in the form of slag, dust, mill scale, grindings, shot dust, metallic slag fines and sludges, etc. Over half of this is slag which is usually used in aggregates and road materials. The remaining waste mainly comprises iron oxide. By recycling such waste for metal recovery, it may be reclassified as secondary material.
Over the last thirty years, the industry has been required to comply with ever more stringent environmental standards. The dusts and sludges are especially polluted with heavy metals such as lead, zinc, cadmium, chromium and nickel, etc. as a result of processing contaminated scrap metal. Consequently, such dusts and sludges have been classified as hazardous.
Numerous processes have been developed to treat and recycle steel mill secondary materials and waste, but these have failed to provide comprehensive solutions because they only deal with some of the waste and also are very costly. Some of these processes use, for example, plasma arc furnaces, briquetting machines or pelletizing systems.
It is an object of this invention to provide a process for treating steel mill waste inexpensively to produce a product which can be stored safely as a non-polluting secondary material suitable for recycling in various furnaces, for example electric arc furnaces, basic oxygen furnaces or blast furnaces.